Thanks for your help guys, I think this one can be closed out now.
I’ve realised that there’s nothing wrong with my Dr Phybes output. The volume drop i was experiencing was the pretty much only with clean sounds, or into a light OD pedal. An output buffer helps a bit, but only so much. Then I tried a much bigger (0.68uF) output cap in place of the 47n, which made a huge difference. It seems the 47n high pass filter is limiting the low end output, which shows up as a volume drop when strumming a chord. Unfortunately the low end from a big output cap also renders the phase effect almost unoticeable – obviously the circuit designers knew what they were doing 🙂 As a tradeoff I changed out the output cap from 47n to 100n, and now i’m very happy with how it sounds both clean and into OD pedals. I’ve also re-ordered the pedals on my board to minimise the signals loss issues, very happy now. Thanks again